1. Technical Field
This invention generally relates to an antifreeze/coolant composition. More particularly, this invention relates to an antifreeze/coolant composition which excels in corrosion inhibition of metals used in a cooling system for an engine, particularly cast aluminum and cast iron, as well as in inhibition of "cavitation" damage.
2. Background Art
A cooling system for an internal-combustion engine generally uses various metals such as aluminum, cast aluminum, cast iron, steel, brass, solder and copper, which are subject to corrosion over time by water or moist air. In order to inhibit metal corrosion, a metal corrosion inhibiting solution such as an antifreeze/coolant composition containing a metal corrosion inhibitor is generally blended in the cooling liquid or water in the cooling system.
An antifreeze/coolant composition as well as cooling water inherently contains some air dissolved therein, which will generate air bubbles or cavitation within the cooling system due chiefly to local fluidic pressure difference and/or vibrations generated through the cooling system. Metal portions, particularly iron parts, of the cooling system can be damaged or corroded by the bubbles, which is called "cavitation damage".
Conventionally, nitrite is blended in antifreeze/coolant compositions to inhibit generation of cavitation. It is assumed that nitrite blended in the antifreeze/coolant compositions provides protection cover on the metal parts.
Nitrite however is known to produce nitrosoamine, a carcinogenic substance, by chemical reaction with amine salts in the cooling liquid. Although use of nitrite in antifreeze/coolant compositions has given rise to controversy, no other effective and safe substitute to inhibit cavitation existed.
Accordingly, it is an object of the present invention to provide an antifreeze/coolant composition which effectively and safely inhibits both corrosion of metals, particularly cast aluminum and cast iron, and generation of cavitation in a cooling system.